1. Field of the Invention
The present invention relates to a surface lighting device, and particularly to a surface lighting device for a liquid crystal display (LCD) or similar apparatus.
2. The Related Art
A typical LCD device comprises a liquid crystal display panel, and a surface lighting device mounted under the liquid crystal display panel for supplying light beams thereto. The surface lighting device mainly comprises one or more light sources for emitting light beams, and a light guide plate. The light guide plate receives the emitted light beams via a light incident surface thereof, and emits the light beams via a light output surface thereof in order to uniformly illuminate the liquid crystal display panel.
Conventionally, there are two types of light sources used in a surface light device of an LCD: a linear source such as a cold cathode fluorescent lamp (CCFL), and a point light source such as a light emitting diode (LED). In general, it is more difficult to obtain uniform illumination when using a point light source compared with using a linear source, due to the divergent angles of light emitted from the point light source. For example, LEDs used as light sources emit light beams having a divergent angle in the range from 30° to 130°. Thus, a light guide plate using LEDs as light sources generally yields a plurality of dark areas between adjacent LEDs. U.S. Pat. No. 6,502,948 (“the '948 patent”) issued to Iwatsuki discloses a conventional surface lighting device which overcomes the above-mentioned problem. Referring to FIG. 9 of the '948 patent, a surface lighting device includes a stick light guide body 16 mounted between two LEDs 20a, 20b for transferring light beams emitting from the LEDs 20a, 20b into a light guide plate 12. The stick light guide body 16 is parallel to a light incident surface of the light guide plate 12, and a length of the stick light guide body 16 approximately coincides with a length of the light incident surface. This configuration has the LEDs 20a, 20b cooperating with the stick light guide body 16 to provide light beams. That is, the combination functions as a linear light source to provide uniform light beams, and does not cause dark areas.
However, in the above-described configuration, one stick light guide body 16 needs two LEDs cooperating therewith, which increases costs. In addition, as seen in FIGS. 7(B) and 9–11 of the '948 patent, since a light emitting surface E1 of the LED 20a is positioned outside the light stick guide body 16, light leakage therebetween occurs. That is, the stick light guide body 16 cannot completely utilize the light beams emitted from LEDs 20a, 20b. Furthermore, the LEDs 20a, 20b and the stick light guide body 16 are provided at one side of the light guide plate 12 only. It is therefore relatively difficult for the surface lighting device to produce uniform emitting light.
It is desired to provide an improved surface lighting device for use in a liquid crystal display device which overcomes the above-described problems.